JP4106529B2 - Exhaust purification device for multi-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for a multi-cylinder internal combustion engine, and more particularly, to a deterioration determination technique for a catalytic converter.
[0002]
[Related background]
In an exhaust purification catalytic converter, the oxygen storage capacity added to the catalyst has a high correlation with the catalyst performance (mainly HC purification performance), so that the catalyst particularly contains a large amount of oxygen storage material such as ceria (Ce). In the converter, as a catalyst deterioration detection method, a method of determining deterioration of the catalytic converter by monitoring a change with time of the oxygen storage capacity is adopted.
[0003]
In this catalyst deterioration detection method, if the exhaust air-fuel ratio flowing into the catalytic converter is modulated with a predetermined period and amplitude between the lean air-fuel ratio and the rich air-fuel ratio, oxygen is stored in the catalytic converter if the oxygen storage capacity is high. The response of the exhaust air / fuel ratio downstream of the catalyst is slow or the amplitude is small, while when the oxygen storage capacity is low, the oxygen is exhausted without being stored in the catalytic converter so that the response of the exhaust air / fuel ratio downstream of the catalyst is fast or the amplitude For example, an oxygen sensor (O ₂ Sensor) or air-fuel ratio sensor (LAFS) detects the fluctuation period, amplitude, etc. of the oxygen concentration output value. If the detected value is equal to or greater than a predetermined reference value, the oxygen storage capacity is reduced, that is, the catalytic converter is deteriorated. I am trying to judge.
[0004]
[Problems to be solved by the invention]
By the way, in recent years, further improvement in exhaust gas purification performance has been demanded from the viewpoint of environmental conservation, and it is required to detect even a slight deterioration of the catalytic converter.
However, in the above conventional catalyst deterioration detection method, the modulation cycle is set to be relatively short because of the relationship with the operation performance of the internal combustion engine. In such a modulation cycle, since the actual amount of stored oxygen is small, this small amount of storage is stored. The catalyst deterioration cannot be detected unless the oxygen storage capacity is reduced to the oxygen amount. That is, although a certain degree of deterioration can be detected, it is difficult to detect a slight catalyst deterioration of a certain degree or less.
[0005]
Therefore, it is conceivable to increase the modulation period. However, if the modulation period is increased in this way, oxygen is occluded sufficiently to exceed the oxygen storage capacity, so that the oxygen concentration output value fluctuation period, amplitude, etc. While the change can be reliably detected and even a slight catalyst deterioration can be detected, there is a problem that the NOx purification performance deteriorates.
[0006]
That is, referring to FIG. 5, there is shown the relationship between the exhaust NOx and the modulation frequency when the center air-fuel ratio is changed when the exhaust air-fuel ratio is modulated. In FIG. (The frequency is high). The cycle increases in the order of □, △, and ▲, and ■ indicates the longest cycle (the frequency is low). When the frequency is lowered, the NOx emission amount is reduced when the center air-fuel ratio is a lean air-fuel ratio side, while NOx emission increases conversely on the rich air-fuel ratio side.
[0007]
Further, when the period is increased (frequency is decreased), although not shown in FIG. 5, there may be a problem that NOx emission increases regardless of the center air-fuel ratio.
The present invention has been made to solve such problems, and an object of the present invention is to provide a multi-cylinder internal combustion engine that can reliably determine even a slight deterioration of a catalytic converter while ensuring exhaust purification performance. An object is to provide an exhaust emission control device.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a plurality of upstream exhaust passages provided for each of a plurality of cylinder groups of a multi-cylinder internal combustion engine and the plurality of upstream exhaust passages are collectively extended. A plurality of downstream exhaust passages and a plurality of upstream exhaust passages disposed in the plurality of upstream exhaust passages, respectively. Upstream three-way catalytic converter And disposed in the downstream exhaust passage Downstream three-way catalytic converter And the upstream exhaust passage Upstream three-way catalytic converter An upstream side exhaust sensor that detects an exhaust air / fuel ratio, and an exhaust air / fuel ratio of exhaust gas flowing into one upstream side exhaust passage of the plurality of upstream side exhaust passages and the other upstream side Exhaust air / fuel ratio changing means for alternately switching the exhaust air / fuel ratio of the exhaust gas flowing into the exhaust passage between a rich air / fuel ratio and a lean air / fuel ratio at predetermined intervals, and an output change of the exhaust air / fuel ratio detected by the upstream exhaust sensor Based on the above Upstream three-way catalytic converter Deterioration determining means for determining deterioration of the Upstream three-way catalytic converter A period in which the exhaust air-fuel ratio of the exhaust gas flowing into the Upstream three-way catalytic converter Set the period when the amount of oxygen occluded in the oxygen storage capacity exceeds, Downstream three-way catalytic converter The period in which the exhaust air-fuel ratio flowing into the engine is switched between the rich air-fuel ratio and the lean air-fuel ratio is set shorter than the predetermined period.
[0009]
Accordingly, the exhaust air / fuel ratio changing means, for example, sets each cylinder of the upstream exhaust passage side cylinder group of the plurality of upstream exhaust passages to the same combustion air / fuel ratio, and sets the other upstream exhaust passage side cylinder groups to the same combustion air / fuel ratio. Each cylinder has the same combustion air-fuel ratio, and the exhaust air-fuel ratio of exhaust gas flowing into one upstream exhaust passage and the exhaust air-fuel ratio of exhaust gas flowing into another upstream exhaust passage are rich and lean air-fuel ratios at a predetermined cycle. And alternately Upstream three-way catalytic converter During the period when the exhaust air-fuel ratio of the exhaust gas flowing into the Upstream three-way catalytic converter Since the amount of oxygen occluded in the exhaust gas is set in a period exceeding the oxygen storage capacity, it is possible to reliably detect a change with time in the output of the exhaust air / fuel ratio detected by the upstream exhaust sensor, Upstream three-way catalytic converter It is possible to detect deterioration of the image.
[0010]
On the other hand, if the modulation period becomes longer, NOx may not be sufficiently purified as described above, but the downstream exhaust passage Downstream three-way catalytic converter As for the exhaust gas from the cylinder group on the one upstream exhaust passage side and the exhaust gas from the cylinder group on the other upstream exhaust passage side alternately flow, the modulation cycle of the rich air-fuel ratio and the lean air-fuel ratio becomes To shorten Upstream three-way catalytic converter NOx that could not be purified Downstream three-way catalytic converter Is surely purified.
[0011]
This ensures exhaust purification performance Three-way catalytic converter It is possible to reliably determine even a slight deterioration of.
According to a second aspect of the present invention, a plurality of the upstream exhaust sensors are provided individually for each of the plurality of upstream exhaust passages, and the deterioration determining means is detected by the plurality of upstream exhaust sensors. The plurality of exhaust air / fuel ratios based on the output change Upstream three-way catalytic converter It is characterized by determining deterioration every time.
[0012]
Therefore, by providing the upstream exhaust sensor individually for each of the plurality of upstream exhaust passages, Upstream three-way catalytic converter All about Upstream three-way catalytic converter It is possible to reliably determine deterioration every time.
According to a third aspect of the present invention, the output change of the exhaust air / fuel ratio detected by the upstream side exhaust sensor is a change over time in the amplitude of the output oscillation caused by switching of the exhaust air / fuel ratio by the exhaust air / fuel ratio changing means. It is characterized by.
[0013]
That is, as mentioned above, Three-way catalytic converter If the exhaust air-fuel ratio flowing into the engine is modulated between the lean air-fuel ratio and the rich air-fuel ratio, oxygen is increased if the oxygen storage capacity is high. Three-way catalytic converter Oxygen is stored in the catalyst, so the amplitude of the exhaust air / fuel ratio downstream of the catalyst is small. Three-way catalytic converter Since the exhaust air / fuel ratio amplitude downstream of the catalyst increases because the exhaust gas is exhausted without being stored in the catalyst, monitoring the change over time in the amplitude of the output vibration of the exhaust air / fuel ratio detected by the upstream exhaust sensor , Upstream three-way catalytic converter It is possible to reliably determine slight degradation of the.
[0014]
According to a fourth aspect of the present invention, the output change of the exhaust air / fuel ratio detected by the upstream side exhaust sensor is a change with time of the response delay time of the output oscillation caused by the switching of the exhaust air / fuel ratio by the exhaust air / fuel ratio changing means. It is characterized by being.
That is, as mentioned above, Three-way catalytic converter If the exhaust air-fuel ratio flowing into the engine is modulated between the lean air-fuel ratio and the rich air-fuel ratio, the oxygen can Three-way catalytic converter Oxygen is stored in the catalyst, so the response of the exhaust air / fuel ratio downstream of the catalyst is slow. Three-way catalytic converter The exhaust air-fuel ratio downstream of the catalyst becomes faster because it is discharged without being stored in the catalyst, so the change over time in the response delay time of the output vibration of the exhaust air-fuel ratio detected by the upstream exhaust sensor is monitored. With that Upstream three-way catalytic converter It is possible to reliably determine slight degradation of the.
[0015]
In the invention of claim 5, the downstream exhaust passage further includes the Downstream three-way catalytic converter A downstream side exhaust sensor that detects an exhaust air / fuel ratio, and the deterioration determining means is based on an output change of the exhaust air / fuel ratio detected by the downstream side exhaust sensor. Downstream three-way catalytic converter It is also characterized in that the deterioration is also determined.
[0016]
Therefore, Downstream three-way catalytic converter Is exposed to high temperature and high pressure exhaust gas Upstream three-way catalytic converter It is harder to deteriorate than Downstream three-way catalytic converter As for the above, deterioration can be determined as before, and the reliability of the exhaust emission control device is improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust emission control device for a multi-cylinder internal combustion engine according to the present invention, and the configuration of the exhaust emission control device will be described below.
As shown in the figure, an engine main body (hereinafter simply referred to as an engine) 1 that is a multi-cylinder internal combustion engine, for example, in a compression stroke together with fuel injection in an intake stroke (intake stroke injection) by switching a fuel injection mode. An in-cylinder injection type spark ignition type 4-cycle 4-cylinder gasoline engine capable of performing the fuel injection (compression stroke injection) is employed. The in-cylinder injection type engine 1 can be operated at a rich air-fuel ratio (rich air-fuel ratio operation) or a lean air-fuel ratio operation (lean air-fuel ratio operation) in addition to the operation at the stoichiometric air-fuel ratio (stoichio). It is.
[0018]
As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber. .
An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. Further, a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 into the combustion chamber at a desired fuel pressure.
[0019]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. The intake manifold 10 is provided with an electromagnetic throttle valve 14 for adjusting the intake air amount.
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 20 is connected to communicate with each exhaust port. Here, as the exhaust manifold 20, a dual type exhaust manifold system as shown in FIG. 2 is employed.
[0020]
In the exhaust manifold 20 comprising this dual type exhaust manifold system, an exhaust passage 20a from the # 1 cylinder, an exhaust passage 20d from the # 4 cylinder, an exhaust passage 20b from the # 2 cylinder, and an exhaust passage 20c from the # 3 cylinder are respectively provided. They are configured to join (when the combustion order is # 1 → # 3 → # 4 → # 2). That is, the # 1 and # 4 cylinders that do not continue combustion are combined into one cylinder group (# 1, # 4 cylinder group), and the # 2 and # 3 cylinders that also do not continue combustion are combined with another cylinder group (# 2). , # 3 cylinder group). Thereby, there is less exhaust interference in the exhaust manifold 20, and a great effect of exhaust inertia or exhaust pulsation can be obtained.
[0021]
An exhaust pipe (downstream exhaust passage) 28 is connected to the other end of the exhaust manifold 20 via a collection pipe (upstream exhaust passage) 22. The collection pipe 22 is connected to the exhaust passage 20a and the exhaust passage 20d. Two pipes (dual pipes) of a collecting pipe (one upstream exhaust passage) 22a through which exhaust gas flows and a collecting pipe (other upstream exhaust passage) 22b through which exhaust gas from the exhaust passage 20b and the exhaust passage 20c flows ). That is, in the collecting pipe 22, exhaust gas from one cylinder group consisting of # 1 cylinder and # 4 cylinder flows through the collecting pipe 22a, and exhaust gas from another cylinder group consisting of # 2 cylinder and # 3 cylinder is collected in the collecting pipe 22b. It is configured to flow through.
[0022]
The collecting pipe 22a includes a three-way catalyst (an upstream catalyst converter, a manifold catalyzer converter, including an oxygen storage material such as ceria (Ce) as an upstream catalyst converter corresponding to the # 1 and # 4 cylinder groups. (Hereinafter referred to as # 1, # 4MCC, or simply MCC) 24, and similarly, the collecting pipe 22b also has oxygen such as ceria (Ce) as an upstream side catalytic converter corresponding to the # 2, # 3 cylinder group. A three-way catalyst (an upstream catalytic converter, hereinafter referred to as # 2, # 3 MCC, or simply abbreviated as MCC) 26 is interposed. When the MCCs 24 and 26 are interposed in the collecting pipe 22a and the collecting pipe 22b as described above, the MCCs 24 and 26 can be activated early even if the engine 1 is in a cold state because the MCCs 24 and 26 are located close to the engine 1. Therefore, it is possible to satisfactorily purify harmful substances (HC, CO, NOx, etc.) in the exhaust gas regardless of the operating state.
[0023]
# 1, # 4 In the upstream part of the MCC 24, that is, the merging part of the exhaust passage 20a and the exhaust passage 20d of the exhaust manifold 20, and in the upstream part of # 2, # 3 MCC 26, that is, the merging part of the exhaust passage 20b of the exhaust manifold 20 and the exhaust passage 20c. Is an air-fuel ratio sensor (LAFS, O) that detects an exhaust air-fuel ratio (exhaust A / F) as an exhaust sensor. ₂ 21a and 21b (hereinafter referred to as front A / F sensors).
[0024]
Further, a similar air-fuel ratio sensor (upstream exhaust sensor, hereinafter referred to as a middle A / F) is also provided in the downstream portion of the collecting pipe 22a from # 1 and # 4MCC24 and the downstream portion of # 2 and # 3MCC26 in the collecting pipe 22b. (Referred to as sensors) 25 and 27, respectively.
Further, a three-way catalyst (a downstream catalyst converter, which is an underfloor catalyzer converter, hereinafter abbreviated as UCC) 30 is interposed in the exhaust pipe 28 as a downstream catalyst converter. The UCC 30 also contains an oxygen storage material such as ceria (Ce).
[0025]
An air-fuel ratio sensor (hereinafter referred to as an upstream rear A / F sensor) 29 as an exhaust sensor is provided at an upstream portion of the UCC 30 of the exhaust pipe 28, and a similar air-fuel ratio sensor (downstream exhaust gas) is also provided at a downstream portion of the UCC 30. A sensor 31 (hereinafter referred to as a downstream rear A / F sensor) 31 is provided.
The electronic control unit (ECU) 60 includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Overall control of the exhaust emission control device is performed.
[0026]
On the input side of the ECU 60, the front A / F sensors 21 a and 21 b, the middle A / F sensors 25 and 27, the upstream rear A / F sensor 29, the downstream rear A / F sensor 31, the crank angle sensor 62, etc. These sensors are connected, and detection information from these sensors is input. When the crank angle is detected by the crank angle sensor 62, the current combustion cylinder is determined based on the crank angle, and the engine speed Ne is obtained.
[0027]
On the other hand, on the output side of the ECU 60, various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14 are connected. For example, the combustion order (based on detection information from each A / F sensor) When the combustion air-fuel ratio (combustion A / F) is set in # 1 → # 3 → # 4 → # 2), the fuel injection amount and the fuel injection timing command signal are fueled in the order of combustion in accordance with the combustion A / F. While being output to the injection valve 6, a command signal for the intake air amount is output to the throttle valve 14, and a command signal for ignition timing is output to the ignition coil 8 in the order of combustion. Accordingly, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, the throttle valve 14 is set to an appropriate opening degree, and spark ignition is performed at an appropriate timing by the spark plug 4.
[0028]
Hereinafter, the operation of the exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to the present invention configured as described above, that is, the determination method for determining catalyst deterioration according to the present invention will be described.
In the catalyst deterioration determination according to the present invention, basically, the exhaust A / F flowing into the catalytic converter is modulated between the lean air-fuel ratio and the rich air-fuel ratio as in the conventional case, and the oxygen storage capacity of the catalytic converter at this time is determined. The deterioration of the catalytic converter is determined by monitoring the change with time. However, in the present invention, unlike the conventional case, the combustion A / F on the # 1, # 4 cylinder group side and the combustion A / F on the # 2, # 3 cylinder group side are set to the lean air-fuel ratio side or the rich air space at regular intervals. The exhaust A / F on the # 1, # 4 cylinder group side and the exhaust A / F on the # 2, # 3 cylinder group side are modulated to a lean air-fuel ratio and a rich air-fuel ratio by switching to the fuel ratio side. .
[0029]
That is, the fuel is supplied so that the # 1 cylinder and the # 4 cylinder have the same combustion A / F, and the # 2 cylinder and the # 3 cylinder have the same combustion A / F. The fuel supply amount to the cylinder and the fuel supply amounts to the cylinders # 2 and # 3 are increased or decreased at regular intervals, for example, at regular intervals.
Referring to FIG. 3, a control routine for determining catalyst deterioration according to the present invention is shown in a flowchart, and the determination procedure for determining catalyst deterioration according to the present invention will be described in detail below along the flowchart.
[0030]
When the catalyst deterioration determination is started, first, in step S10, whether or not the combustion A / F and the exhaust A / F on the side of the # 1, # 4 cylinder group side is the lean A / F continues for a predetermined period T1. Determine. The predetermined period T1 is a map value (for example, about 2 to 6 seconds) obtained in advance according to operating conditions (engine rotational speed Ne, volumetric efficiency, catalyst temperature, etc.), but may be a fixed value. It is sufficient that it is longer than the cycle. Preferably, when the exhaust A / F is lean A / F, the period until the amount of oxygen stored in the # 1, # 4 MCC 24 exceeds the oxygen storage capacity, that is, the modulation of the exhaust A / F Is suitably set according to the oxygen storage capacity of # 1 and # 4MCC 24 so as to be longer than the period until it is detected by the middle A / F sensor 25. In this case, the operating conditions of the engine 1 (engine rotational speed Ne, volume efficiency, catalyst temperature, exhaust temperature, average illustrated effective value are set so that the exhaust purification performance of # 1 and # 4MCC24 is optimized or the deterioration is easily detected. It is preferable to correct the predetermined period T1 according to the pressure, the net average effective pressure, the intake manifold pressure, the cooling water temperature, whether or not the engine is within the predetermined period at the start, and the degree of catalyst deterioration (travel distance, etc.).
[0031]
Here, the predetermined period T1 is defined by time, but may be defined by the number of cycles of the engine 1, for example, 150 cycles.
If the determination result in step S10 is false (No) and the period during which the combustion A / F on the # 1, # 4 cylinder group side is lean A / F has not reached the predetermined time T1, the process proceeds to step S12. For the # 1, # 4 cylinder group side, the combustion A / F is modulated to the lean A / F side, and for the # 2, # 3 cylinder group side, the combustion A / F is modulated to the rich A / F side.
[0032]
On the other hand, if the determination result in step S10 is true (Yes) and it is determined that the period during which the combustion A / F on the # 1, # 4 cylinder group side is the lean A / F exceeds the predetermined time T1, the step Proceeding to S14, this time, it is determined whether or not the period in which the combustion A / F on the # 2, # 3 cylinder group side is the lean A / F continues for a predetermined period T2. Here, the predetermined period T2 is set to a map value (for example, about 2 to 6 seconds) obtained in advance according to operating conditions (engine rotational speed Ne, volumetric efficiency, catalyst temperature, etc.) as in the predetermined period T1. The fixed value may be longer than one cycle. Preferably, as described above, when the exhaust A / F is lean A / F, the amount of oxygen stored in the # 2 and # 3 MCCs 26 is the oxygen storage. The period until the capacity is exceeded, that is, the period until the modulation of the exhaust A / F is detected by the middle A / F sensor 27, is set as appropriate according to the oxygen storage capacity of the # 2 and # 3 MCCs 26. Is good. In this case, the operating conditions of the engine 1 (engine rotational speed Ne, volumetric efficiency, indicated mean effective pressure, net mean effective so that the exhaust purification performance of # 2, # 3 MCC 26 can be optimized or deterioration can be easily detected. It is preferable to correct the predetermined period T2 according to the pressure, the intake manifold pressure, the coolant temperature, whether or not the engine is within the predetermined period at the start, and the degree of catalyst deterioration (travel distance, etc.).
[0033]
Here, the predetermined period T2 is set to be the same as the predetermined period T1, but the predetermined period T2 and the predetermined period T1 may be different periods, and the predetermined period T2 is defined by the number of cycles of the engine 1 as described above. For example, 150 cycles may be used.
If the determination result in step S14 is false (No) and the period during which the combustion A / F on the # 2, # 3 cylinder group side is lean A / F has not reached the predetermined time T2, the process proceeds to step S16. For the # 1, # 4 cylinder group side, the combustion A / F is modulated to the rich A / F side, and for the # 2, # 3 cylinder group side, the combustion A / F is modulated to the lean A / F side. On the other hand, if the determination result of step S14 is true (Yes), the process returns to step S10 again, and the above determination is repeated.
[0034]
That is, referring to FIG. 4, when the control routine is executed, the exhaust A / F for each cylinder and the exhaust A / F for each cylinder group (R and the solid line indicate the rich air-fuel ratio side, and L and the broken line indicate the lean Although the time change of the air-fuel ratio side is shown in the time chart, here, as shown in the figure, # 1, # over a predetermined period T1 (here, for example, 4 cycles for convenience of explanation) Once the 4-cylinder group side is modulated to the lean A / F side # 2 and the # 3 cylinder group side to the rich A / F side, then the # 1, # 4 cylinder group side over a predetermined period T2 (for example, 4 cycles) Is adjusted to # 2 on the rich A / F side, and the # 3 cylinder group side is modulated to the lean A / F side, and exhaust A / F of exhaust gas flowing into # 1, # 4 MCC24 and # 2, # 3 MCC26 flow into Exhaust gas A / F is a relatively long period (T1 + T2, here 8 cycles) (1)), and the modulation is performed alternately (exhaust air / fuel ratio changing means).
[0035]
As described above, when the exhaust A / F of the exhaust gas flowing into the # 1, # 4MCC24, # 2, and # 3MCC26 is modulated with a relatively long predetermined period, if the catalyst has deteriorated so that the catalyst deterioration should be detected, lean The amount of oxygen stored in # 1, # 4MCC24, # 2, and # 3MCC26 at the air-fuel ratio exceeds the oxygen storage capacity, and the modulation of exhaust A / F is always ensured by the middle A / F sensors 25 and 27. Can be detected. When the exhaust A / F modulation can always be detected reliably, the decrease in the oxygen storage capacity of # 1, # 4MCC24, # 2, and # 3MCC26 is easily caused by the output change of these middle A / F sensors 25 and 27. By detecting the output change of the middle A / F sensors 25 and 27, the oxygen storage capacity of # 1, # 4MCC24 and # 2 and # 3MCC26 is slightly reduced, that is, # 1, # 4MCC24 and # 2 Thus, it is possible to reliably detect even a slight deterioration of # 3MCC26.
[0036]
If step S12 or step S16 is performed, it will be detected in step S18 whether the output of the middle A / F sensors 25 and 27 has changed. Specifically, when the oxygen storage capacity is reduced, the amount of oxygen discharged without being occluded increases, or oxygen reaches a saturation amount at an early stage and begins to flow out, so that the middle A / F sensors 25 and 27 A change over time in the amplitude of the output vibration or a change over time in the response delay time of the output vibration of the middle A / F sensors 25 and 27 is detected.
[0037]
In step S20, it is determined whether or not a change with time has occurred in the amplitude of the output vibration of the middle A / F sensors 25 and 27, or the response delay time. That is, it is determined whether the amount of discharged oxygen has increased and the amplitude has not increased to a predetermined value or more, or whether the response delay time has become a predetermined time or less and oxygen has not flowed out early. If the determination result is true (Yes) and it is determined that the amplitude of the output vibration of the middle A / F sensors 25 and 27 or the response delay time has changed over time, the process proceeds to step S22, and # 1, It is determined that # 4MCC24 or # 2, # 3MCC26 has deteriorated (deterioration determination means). Specifically, when it is determined that the amplitude of the output vibration of the middle A / F sensor 25 or the response delay time has changed with time, it is determined that # 1 and # 4 MCC 24 have deteriorated, and the middle A / F If it is determined that the amplitude of the output vibration of the F sensor 27 or the response delay time has changed with time, it is determined that # 2 and # 3 MCC 26 have deteriorated.
[0038]
When the determination is made based on the response delay time, it is preferable to correct by subtracting the time until the exhaust gas reaches the middle A / F sensors 25 and 27.
On the other hand, if it is determined that the amplitude of the output vibration of the middle A / F sensors 25, 27 or the response delay time has not changed with time, the process proceeds to step S24, where # 1, # 4MCC24, # 2, # 2, It is determined that the 3MCC 26 is functioning normally without deterioration.
[0039]
By the way, if the exhaust A / F of the exhaust gas flowing into # 1, # 4MCC24, # 2, # 3MCC26 is modulated with a relatively long predetermined period, NOx is sufficient in # 1, # 4MCC24, # 2, # 3MCC26 It will not be purified. However, referring to FIG. 4 above, the time change of the exhaust A / F upstream of the UCC 30 is also shown. As shown in FIG. 4, the exhaust gases from the collecting pipe 22a and the collecting pipe 22b flow together. In the upstream portion of the UCC 30, the exhaust A / F is the exhaust A / F of the exhaust gas discharged from each cylinder, and the modulation cycle of the exhaust A / F of the exhaust gas flowing into the UCC 30 is shortened. The NOx that could not be purified by the # 1, # 4MCC 24, # 2, and # 3MCC 26 is reliably purified by the UCC 30.
[0040]
That is, according to the determination method of catalyst deterioration determination according to the present invention, the slight deterioration of # 1, # 4MCC24, # 2, and # 3MCC26 is ensured while ensuring the purification performance of NOx as well as HC and CO. It becomes possible to judge.
In step S26, it is detected in the same manner as in step S18 whether the output of the downstream rear A / F sensor 31 has changed. That is, a change with time in the amplitude of the output vibration of the downstream rear A / F sensor 31 or a change with time in the response delay time of the output vibration of the downstream rear A / F sensor 31 is detected.
[0041]
In step S28, as in step S20, it is determined whether or not a change with time has occurred in the amplitude of the output vibration of the downstream rear A / F sensor 31 or the response delay time. If the determination result is true (Yes) and it is determined that the amplitude of the output vibration of the downstream rear A / F sensor 31 or the response delay time has changed with time, the process proceeds to step S30 and the UCC 30 deteriorates. (Deterioration determination means). On the other hand, if it is determined that the output vibration amplitude and response delay time of the downstream rear A / F sensor 31 have not changed with time, the process proceeds to step S32, where it is determined that the UCC 30 is functioning normally without deterioration. To do.
[0042]
As for the UCC 30, as described above, since the modulation cycle of the exhaust A / F of the exhaust gas flowing into the UCC 30 is shortened, it includes conventional problems, and the degradation determination accuracy is the above-described # 1, # 4 MCC 24, and # 2, # 3 Not as high as MCC26. However, since the UCC 30 also has at least the same deterioration determination accuracy as the conventional one, the deterioration determination of the UCC 30 is performed together with the deterioration determination of the # 1, # 4MCC 24, # 2, and # 3 MCC 26, so that the exhaust gas is exhausted. The reliability of the entire purification device can be improved.
[0043]
The description of the embodiment is finished as above, but the present invention is not limited to the above embodiment.
For example, when performing catalyst deterioration determination, it is preferable to feedback control the exhaust A / F that flows into # 1, # 4MCC24, # 2, and # 3MCC26, respectively, based on information from the front A / F sensors 21a and 21b. Further, the exhaust A / F flowing into the UCC 30 may be feedback controlled based on information from the upstream rear A / F sensor 29. Further, the exhaust A / F flowing into the UCC 30 is preferably feedback-controlled based on information from the downstream rear A / F sensor 31, and # 1, # based on information from the middle A / F sensors 25, 27 The exhaust A / F flowing into the 4MCC 24, # 2, and # 3 MCC 26 is preferably feedback-controlled. As a result, the exhaust purification performance can be further improved, and the deterioration determination accuracy of the catalyst can be improved.
[0044]
Further, it is preferable that the determination of catalyst deterioration be performed only when the UCC 30 is in an active state, so that NOx can be reliably purified by the UCC 30. In this case, whether or not the UCC 30 is in an active state is, for example, whether or not the UCC 30 is equal to or higher than a predetermined temperature (for example, 300 ° C.) or the cooling water temperature of the engine 1 is equal to or higher than a predetermined temperature (for example, 40 ° C.). The determination may be made based on whether or not a predetermined time (for example, 3 minutes) has elapsed after the engine 1 is started, or may be determined based on other conditions.
[0045]
Further, the output change of the middle A / F sensor may be of any type as long as it includes amplitude or response delay time.
Further, the catalyst deterioration determination may be performed only during the steady operation of the engine 1, for example. Thereby, it is possible to reliably perform the catalyst deterioration determination without affecting the output performance of the engine 1.
[0046]
In the above embodiment, a cylinder injection type spark ignition type four-cycle four-cylinder gasoline engine is used as the engine 1, but if the engine 1 is multi-cylinder, an intake pipe injection type gasoline engine, a two-cycle gasoline engine, Any engine such as a diesel engine may be used.
[0047]
【The invention's effect】
As described above in detail, according to the exhaust purification device of a multi-cylinder internal combustion engine of claim 1 of the present invention, for example, each cylinder of the cylinder group on the upstream exhaust passage side of one of the plurality of upstream exhaust passages Are set to the same combustion air-fuel ratio, and each cylinder of the cylinder group on the other upstream exhaust passage side is set to the same combustion air-fuel ratio, and flows into one upstream exhaust passage and the other upstream exhaust passage. The exhaust air-fuel ratio of the exhaust gas to be switched alternately between the rich air-fuel ratio and the lean air-fuel ratio at a predetermined cycle, Upstream three-way catalytic converter During the period when the exhaust air-fuel ratio of the exhaust gas flowing into the Upstream three-way catalytic converter Since the amount of oxygen occluded is set to a period that exceeds the oxygen storage capacity, Upstream three-way catalytic converter Can be detected reliably, while the downstream exhaust passage Downstream three-way catalytic converter If you look at the short, the modulation cycle between the rich air-fuel ratio and the lean air-fuel ratio is shortened. Upstream three-way catalytic converter NOx that could not be purified by Downstream three-way catalytic converter Can be purified reliably.
[0048]
This ensures exhaust purification performance Three-way catalytic converter It is possible to reliably determine even a slight deterioration of.
According to the exhaust gas purification apparatus for a multi-cylinder internal combustion engine of claim 2, by providing the upstream side exhaust sensor individually for each of the plurality of upstream side exhaust passages, Upstream three-way catalytic converter All about Upstream three-way catalytic converter It is possible to reliably determine deterioration every time.
[0049]
According to the exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to claim 3, by monitoring the change over time in the amplitude of the output vibration of the exhaust air-fuel ratio detected by the upstream side exhaust sensor, Upstream three-way catalytic converter It is possible to reliably determine slight degradation of the.
According to the exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to claim 4, by monitoring the change over time in the response delay time of the output vibration of the exhaust air / fuel ratio detected by the upstream side exhaust sensor, Upstream three-way catalytic converter It is possible to reliably determine slight degradation of the.
[0050]
According to the exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to claim 5, Downstream three-way catalytic converter As for the above, deterioration can be determined as before, and the reliability of the exhaust emission control device can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust emission control device for a multi-cylinder internal combustion engine according to the present invention.
FIG. 2 is a diagram showing a dual type exhaust manifold system.
FIG. 3 is a flowchart showing a control routine for determining catalyst deterioration according to the present invention.
FIG. 4 is a time chart showing temporal changes in the exhaust A / F for each cylinder, the exhaust A / F for each cylinder group, and the exhaust A / F upstream of the UCC when a catalyst deterioration determination control routine is executed. .
FIG. 5 is a diagram showing the relationship between exhaust NOx and modulation frequency when the center air-fuel ratio is changed when the exhaust air-fuel ratio is modulated.
[Explanation of symbols]
1 engine
6 Fuel injection valve
20 Exhaust manifold
22a Collecting pipe (one upstream exhaust passage)
22b Collecting pipe (other upstream exhaust passage)
24 Three-way catalyst (MCC, upstream catalytic converter)
25 Middle A / F sensor (upstream exhaust sensor)
26 Three-way catalyst (MCC, upstream catalytic converter)
27 Middle A / F sensor (upstream exhaust sensor)
28 Exhaust pipe (downstream exhaust passage)
30 Three-way catalyst (UCC, downstream catalytic converter)
31 Downstream rear A / F sensor (downstream exhaust sensor)
60 Electronic control unit (ECU)

Claims (5)

A plurality of upstream exhaust passages provided for a plurality of cylinder groups of the multi-cylinder internal combustion engine;
A downstream exhaust passage extending from the plurality of upstream exhaust passages;
A plurality of upstream three-way catalytic converters respectively disposed in the plurality of upstream exhaust passages;
A downstream three-way catalytic converter disposed in the downstream exhaust passage;
An upstream exhaust sensor that is provided downstream of the upstream three-way catalytic converter in the upstream exhaust passage and detects an exhaust air-fuel ratio;
The exhaust air / fuel ratio of exhaust gas flowing into one upstream exhaust passage of the plurality of upstream exhaust passages and the exhaust air / fuel ratio of exhaust gas flowing into another upstream exhaust passage at a predetermined cycle are rich air / fuel ratio and lean air / fuel ratio. An exhaust air / fuel ratio changing means for alternately switching to the fuel ratio;
A deterioration determining means for determining deterioration of the upstream side three-way catalytic converter based on an output change of the exhaust air / fuel ratio detected by the upstream side exhaust sensor;
With
Period for the exhaust air-fuel ratio of the exhaust gas flowing into the upstream three-way catalytic converter and lean air-fuel ratio, with the amount of oxygen stored in the upstream three-way catalytic converter is set to a period exceeding the oxygen storage capacity ,
An exhaust emission control device for a multi-cylinder internal combustion engine, characterized in that a cycle in which an exhaust air-fuel ratio flowing into the downstream side three-way catalytic converter switches between a rich air-fuel ratio and a lean air-fuel ratio is set shorter than the predetermined cycle. A plurality of the upstream exhaust sensors are provided individually for each of the plurality of upstream exhaust passages, and the deterioration determining means is configured to detect an output change of the exhaust air-fuel ratio detected by the plurality of upstream exhaust sensors. 2. The exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein deterioration is determined for each of the plurality of upstream side three-way catalytic converters .   The output change of the exhaust air / fuel ratio detected by the upstream side exhaust sensor is a change over time in the amplitude of output oscillation caused by switching of the exhaust air / fuel ratio by the exhaust air / fuel ratio changing means. 2. An exhaust emission control device for a multi-cylinder internal combustion engine according to 2.   The output change of the exhaust air / fuel ratio detected by the upstream side exhaust sensor is a change over time in a response delay time of output vibration caused by switching of the exhaust air / fuel ratio by the exhaust air / fuel ratio changing means. 3. An exhaust emission control device for a multi-cylinder internal combustion engine according to 1 or 2. Furthermore, the downstream exhaust passage is provided with a downstream exhaust sensor that is located downstream of the downstream three-way catalytic converter and detects an exhaust air-fuel ratio,
The degradation determination means may also be determined together with the deterioration of the downstream three-way catalytic converter based on the output change of the exhaust air-fuel ratio detected by the downstream exhaust sensor, according to claim 1 to 4 An exhaust emission control device for a multi-cylinder internal combustion engine according to any one of the above.

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